The present invention relates to microactuators and micromotors and methods for operating microactuators and micromotors, all generally referred to herein as microdevices. In particular the invention relates to new and improved transient energy release microdevices of smaller size and improved efficiency operating under nonequilibrium conditions. The term microdevice includes reciprocating devices such as microcompressors and vacuum pumps as well as single stroke actuators and single throw and double throw electrical switches.
The present invention further relates to micromechanical devices and arrays of such devices which are non-volatile, and essentially radiation immune and insensitive to ambient conditions.
Considerable work is presently going on in the field of microdevices, which may be mechanical, electromagnetic, electrostatic, fluid or pneumatic in nature. By way of example, see:
A Microminiature Electric-to-Fluidic Valve, by Zdeblick and Angell in Transducers '87 page 827.
Silicon micromechanics: sensors and actuators on a chip, by Howe and Muller in IEEE Spectrum July 1990 page 29.
Study on Microengines: Miniaturizing Stirling Engines for Actuators, by Nakajima et al in Sensors and Actuators (1989) at page 75.
Uses for microdevices will be readily apparent, including those recited in the above publications and in the references cited therein.
Microdevices, including pumps and tools, have been considered for application in medicine, optics, microassembly, industrial process automation, analytical instruments, photonics and aerospace. The present invention is particularly directed to microdevices utilizing gas pressure for producing high output forces and power by heating and cooling of a gas. Problems arise in this type of microdevice with respect to efficiency because of heat losses to the walls in the gas chambers.
In other pneumatically driven devices supplied with gas through feed lines the pressure drop in such transmission lines will typically be in the tens of atmospheres for a 100 micrometer diameter line one meter long. Sealed devices have been proposed that rely on phase changes of a liquid charge. These devices are relatively slow acting with response times greater than 1 millisecond, whereas response times or cycle times of 10 microseconds are much more attractive for microscale devices.
It is an object of the present invention to provide a new and improved microdevice and method of operation utilizing a gas as the output power source with the gas operating in a nonequilibrium mode to provide reciprocating motion at a high repetition rate, while also operating at high efficiency.
It is a particular object of the invention to provide a microdevice with overall dimensions in the order of 100 micrometers or less while producing output forces in the order of 10.sup.2 to 10.sup.4 dynes and greater at cycle thermal efficiencies on the order of 10%.
It is a further object of the invention to provide such a microdevice wherein the gas in a cell is cyclically and directly heated to increase the gas pressure and provide the output force and is thereafter rapidly cooled to reduce the gas pressure to provide transient output force pulses at cycle times of not more than about 50 microseconds, and under certain circumstances not more than about 5 microseconds.
It is a particular object of the invention to accomplish gas heating by direct heating of the gas itself by photon energy directed into the cell and by electrical discharge in the gas within the cell, and by heating of the gas from the inner wall of the cell with the wall heated by photon energy directed onto the wall and with the wall heated by an electrical resistance film on the inner surface of the wall.
A further object of the invention is to provide such a microdevice in the form of a microactuator for providing a force as an output and in the form of a micropump for operating as a vacuum pump or compressor.
It is an object of the invention to provide a microdevice suitable for operation as an electrical switch and including a bistable membrane dividing the cell into two chambers, with the gas pressure increase being selective in the chambers to move the bistable membrane from one stable position to the other stable position.
An additional object of the invention is to provide micromechanical devices which can be configured as an electrical switch, memory cell, logic gate, and the like, and arrays of such devices, providing products which are non-volatile, and essentially radiation immune and insensitive to ambient conditions. A further object is to provide such items which can be manufactured using silicon process technology. Another object is to provide such devices which are capable of switching at gigahertz rates.
It is a particular object of the invention to provide micromechanical devices which are competitive with conventional CMOS devices in size, speed, and energy consumption for a number of electronic applications. With a characteristic size of approximately 1 micrometer, the devices of the invention are capable of switching states in less than 1 nanosecond using less than 1 picojoule per state change. Further, energy loss through friction is eliminated as there is no sliding contact between moving parts.
Another object of the invention is to provide such devices suitable for manufacture in arrays for use as cross-bar switches, logic elements, and memory cells. An additional object is to provide such devices for use as dynamic mirrors.
A further particular object is to provide such devices which can operate with a sealed pressure chamber and without a sealed pressure chamber, the latter being possible due to the small size and rapid response with state changes occurring before the pressure pulse in the chamber dissipates. In the unsealed chamber version, performance is enhanced by an increase in the rate at which energy is dissipated and an automatic compensation for ambient temperature effects.
Other objects, advantages, features and results will more fully appear in the course of the following description.